Parts conveyor pallet and means for supporting same on an initial pair of rails and switching same to a second pair of rails

ABSTRACT

A pallet for conveying parts through a succession of work stations. The primary support for the pallet comprises a pair of vertically aligned tubular rails. The pallet is support on these rails by a pair of upper rollers mounted on said pallet and riding on the upper rail and a pair of lower rollers mounted on said pallet and riding on the lower rail along with a third pair of intermediate or clamping rollers, shiftably mounted on said pallet, which cooperates with the upper rollers to clamp the pallet to the upper rail. In this manner the pallet is cantilevered from the top rail. The pallet is driven by means of a downwardly extending arm having a spring loaded friction plate which frictionally engages the top of a flat segmented (crescent) chain disposed beneath the pallet and continuously driven by conventional means. The first mentioned rails are disposed in a continuous path. Each work station is mounted to one side of said path. For each work station there is a side pair of vertically aligned rails extending closely adjacent to and parallel to said first mentioned rails a relatively short distance, then leaving said first mentioned rails to lead to a said work station, and then extending back to said first mentioned rails wherein said side pair of rails is again closely adjacent to and parallel to said first mentioned rails a relatively short distance. A second chain, like the chain first described and running at the same speed thereof, is positioned beneath said side pair of rails at the same level as said first chain. The said plate extends beyond said first chain a distance sufficient to engage said second chain when said pallet is brought into proximity with said side pair of rails. Said pallet has mounted thereon a second pair of upper rollers, and a second pair of lower rollers, disposed to engage said side pair of rails when the pallet is brought to that position wherein the side pair of rails is parallel to said first mentioned rails. At this last mentioned point means are actuated to disengage said third pair of rollers from clamping engagement with said first mentioned upper rail while immediately causing a similar pair of clamping rollers to engage the upper of said side pair of rails whereby said pallet is then cantilevered from said side pair of rails by virtue of said second pair of upper rollers, said similar pair of clamping rollers and said second pair of lower rollers. Continued movement of the chains will cause the pallet to move along on the side rails to the work station. Similarly the pallet may be placed back on the first mentioned rails when the side rails are parallel thereto and means are actuated to again reverse the positions of said first mentioned, and said similar, clamping rollers.

United States Patent 1 Lott et al.

[ 1 PARTS CONVEYOR PALLET AND MEANS FOR SUPPORTING SAME ON AN INITIALPAIR OF RAILS AND SWITCHING SAME TO A SECOND PAIR OF RAILS [75]Inventors: George T. Lott, Wyoming; Francis 11. Little, Cincinnati, bothof Ohio [73] Assignee: Lott Tool Company, Cincinnati,

Ohio

[22] Filed: Aug. 16, 1972 [21] Appl. No.: 281,126

Related US. Application Data [62] Division of Ser. No. 139,672, May 3,1971, Pat. No.

[56] References Cited UNITED STATES PATENTS 3,659,529 5/1972 Jacobs104/130 3,033,126 5/1962 Graybeal 104/101 Primary Examiner-Gerald M.Forlenza Assistant ExaminerD. W. Keen Attorney-Melville, Strasser,Foster & Hoffman [57] ABSTRACT A pallet for conveying parts through asuccession of work stations. The primary support for the palletcomprises a pair of vertically aligned tubular rails. The pallet issupport on these rails by a pair of upper rollers mounted on said palletand riding on the upper rail and a pair of lower rollers mounted on saidpallet and riding on the lower rail along with a third pair ofintermediate or clamping rollers, shiftably mounted on said pallet,which cooperates with the upper rollers to clamp the pallet to the upperrail. In this manner the Dec. 11, 1973 pallet is cantilevered from thetop rail. The pallet is driven by means of a downwardly extending armhaving a spring loaded friction plate which frictionally engages the topof a flat segmented (crescent) chain disposed beneath the pallet andcontinuously driven by conventional means. The first mentioned rails aredisposed in a continuous path. Each work station is mounted to one sideof said path. For each work station there is a side pair of verticallyaligned rails extending closely adjacent to and parallel to said firstmentioned rails a relatively short distance, then leaving said firstmentioned rails to lead to a said work station, and then extending backto said first mentioned rails wherein said side pair of rails is againclosely adjacent to and parallel to said first mentioned rails arelatively short distance. A second chain, like the chain firstdescribed and running at the same speed thereof, is positioned beneathsaid side pair of rails at the same level as said first chain. The saidplate extends beyond said first chain a distance sufficient to engagesaid second chain when said pallet is brought into proximity with saidside pair of rails. Said pallet has mounted thereon a second pair ofupper rollers, and a second pair of lower rollers, disposed to engagesaid side pair of rails when the pallet is brought to that positionwherein the side pair of rails is parallel to said first mentionedrails. At this last mentioned point means are actuated to disengage saidthird pair of rollers from clamping engagement with said first mentionedupper rail while immediately causing a similar pair of clamping rollersto engage the upper of said side pair of rails whereby said pallet isthen cantilevered from said side pair of rails by virtue of said secondpair of upper rollers, said similar pair of clamping rollers and saidsecond pair of lower rollers. Continued movement of the chains willcause the pallet to move along on the side rails to the work station.Similarly the pallet may be placed back on the first men- ,tioned railswhen the side rails are parallel thereto and means are actuated to againreverse the positions of said first mentioned, and said similar,clamping rollers.

5 Claims, 7 Drawing Figures PATENTEU DEC 1 1 I975 SHEET 2 UF 3 PARTSCONVEYOR PALLET AND MEANS FOR SUPPORTING SAME ON AN INITIAL PAIR OFRAILS AND SWITCHING SAME TO A SECOND PAIR OF RAILS CROSS REFERENCE TORELATED APPLICATIONS This is a division of application Ser. No. 139,672filed May 3, 1971, now U.S. Pat. No. 3,7l7,l03 issued Feb. 20, 1973.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention haswide application. It is useful in those industries wherein a given partis to have a number of machining operations performed thereon. Thepallet-conveyor of this invention enables such a part to be takensequentially through a number of work stations disposed to one side ofamain track. Although the instant invention is particularly suitable foruse in the automobile industry wherein a number of parts weighing withinthe range of 50 to 150 pounds must undergo successive machiningoperations, it will be obvious to those skilled in the art that thisinvention may have much greater use than that. It will be equallyobvious that with relatively minor adjustments the pallet may be adaptedto convey much lighter or much heavier loads than indicated.

2. Description of the Prior Art No search has been made in the UnitedStates Patent Office to determine whether or not a pallet-conveyorsystem like that comprising the instant invention is shown in any issuedU.S. patent. Although the inventors have a fairly extensive personalknowledge of this general art, they are not aware of any part conveyingpallet arranged for cantilevered support from one set of verticallyaligned rails and shiftable to similar cantilevered support from asecond set of vertically aligned rails while the pallet is driven bycombinations of continuously moving chains and the like.

SUMMARY OF THE INVENTION Heretofore problems have arisen respecting theefficient handling of parts and the like which must have a plurality ofoperations performed thereon. It is expensive and time consuming totransport such parts, step by separate step, from one place to another.It is not always practicable to station the part in one place and changetools one way or another. Mechanisms which have attempted to routepieces for successive operations in the past have proved complicated,subject to timing difficulties and expensive. The present inventionsolves these and other problems by providing a part conveying palletwhich may be supported, selectively, on various sets of verticallyaligned rails, two each. The pallet is provided with two pairs of upperrollers, one pair at either side thereof, and two pairs of lowerrollers, one pair at either side thereof. Intermediate these upper andlower rollers, which are fixed in position on the pallet, is a pair ofshiftable arms linked together for simultaneous movement. Each arm has aclamping roller at either end thereof. In the normal position the palletis supported on the main track comprised of a pair of vertically alignedrails by virtue of the upper and lower rollers stationed on the sameside of the pallet and riding on the upper and lower railscomprisingsaid main track. The corresponding clamping rollers engage theupper rail whereby the pallet is cantilevered from the main track. Whenthe pallet is moved along the main track until such time as the upperand lower rollers on the side opposite the main track come into contactwith those portions of vertically aligned upper and lower railscomprising a side track, the side track being initially parallel to themain track, the pallet thus being supported simultaneously for a briefperiod on both the main track and the side track, the shiftable arms areactuated during such brief period whereby to disengage the clampingrollers from the main track upper rail and to immediately engage theother clamping rollers with the upper rail of the side track whereby thepallet is thereby cantilevered from the side track. During this briefperiod the pallet is driven by both the main track drive and the sidetrack drive, each drive following its respective track, by virtue ofmeans on the the pallet adapted to engage both drives simultaneouslywhen the tracks parallel one another, at such time the tracks alongbeing closely adjacent one another.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of thepallet and conveyor mechanism (partially fragmentary) according to thisinvention,

FIG. 2 is a front elevation taken from the right side of FIG. 1,

FIG. 3 is a schematic plan view showing the general arrangement of themain track and a plurality of side tracks and work stations to beserviced by the palletconveyor system of this invention,

FIG. 4 is a front elevation, with parts broken away, of the pallet andtrack mechanisms including within the scope of this invention showingthe pallet clamped in cantilevered condition on the main, left-handtrack means as viewed in this Figure,

FIG. 5 is a view similar to FIG. 4 but with the pallet clamped incantilevered condition on the side, righthand track means as viewed inthis Figure,

FIG. 6 is a perspective view of portions of the pallet and trackmechanisms, and

FIG. 7 is a view similar to FIG.4 but showing the pallet cantilivered onthe main track in an area of the system wherein there is no side track.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIGS. 6 and3, the basic elements of the involved mechanisms will be described. Theparts conveyor pallet is generally indicated at 10. This pallet 10 isarranged to ride on and along a main track comprised of a pair ofvertically aligned, tubular rails 11a and 11b. From time to time,however, the pallet will ride on and along one or more side tracks eachof which is comprised ofa pair of vertically aligned, tubular rails 12aand 12b. Journaled in the pallet 10 is a first pair of upper rollers 13and a second pair of'upper rollers 14. Also journaled in this pallet 10is a first pair of lower rollers 15 and a second pair of lower rollers16. All of these rollers l3, l4, l5 and 16 are fixed in position on thepallet 10.

Intermediate the pairs of upper and lower rollers is a clamping rollers18 are mounted on the other ends of these arms 19a and 19b. The arms 19aand 1912 are fixed on a rod 20 so that they will move together. The rod20 is suitably journaled in the pallet 10. In the position shown inFIGS. 6 and 7 the clamping rollers 17 are engaged with the upper rail11a so that, by virtue of the rollers 13, 15 and 17, the pallet 10 iscantilevered from the main track comprised of the vertically aligned,tubular rails Ila and 11b. It is true, however, that during the timeportions of the side track rails 12a, 1212 are parallel to the maintrack rails 11a, 11b the rollers 14 and 16 will engage the respectiverails 12a, 12b; this is the condition specifically illustrated in FIG.6. FIG. 7, therefore, shows the pallet 10 as supported from the maintrack rails 11a, 11b either prior to, or after, the pallet is broughtinto the vicinity of any of the side tracks 12a, 12b.

Fixed on one side of the arm 19a is a back piece or cam plate 21. Thisis perhaps best seen in FIGS. 1 and 2. The cam plate 21 has downwardlyprojecting cam portions 22 and 23 located at the opposite ends thereof.A shift bar 24 is slidably arranged in the pallet 10 between a first anda second position. The bar 24 is partially cut away at 25 and 26 toaccommodate a pair of cam rollers 27 and 28 which are journaled on thebar 24. In view of the fact that the bar 19a, the cam plate 21, the rod20 and the bar 19b all move together as a unit when actuated by movementof the bar 24 as will be further described, only one such shiftable bar24 is required.

In the first position of the shiftable bar 24 the roller 27 engages thecam projection 22 whereby to move the cam plate 21 and the arm 190 intosuch position that the clamping rollers 17 engage the upper rail 11a ofthe main conveyor track. This is best seen in FIGS. 2, 4 and 6. In thisposition, as is best seen in FIG. 7, the pallet 10 is cantilevered fromthe main track 11a, 11b by virtue of engagement of the upper rollers 13with the upper tubular member 11a, engagement of the clamping rollers 17with this same tubular member 110, and engagement of the lower rollerswith the lower tubular member 11b. The pair of upper rollers 14 and pairof lower rollers 16 are out of engagement with anything at this point asare also the clamping rollers 18. When, however, the pallet 10 comes toa point wherein the side track rails 12a, 12b are parallel to the maintrack rails 11a, 11b the rollers 14 and 16 are so positioned that theywill contact these side track rails. The clamping rollers 18, however,at the very point the rollers 14 and 16 first come into contact with therails 12a, 12b will be spaced from the rail 12a until the shiftable bar24 is actuated. Thus the main support for the pallet l0 at this pointcontinues to be its cantilevered arrangement with respect to the maintracks rails 11a, 11b.

When the pallet 10 is in position with respect to the main track rails11a, 11b and the side track rails 12a, 12b as indicated in FIGS. 4 and5, this being that stage wherein portions of the rails 11a, 11b, 12a and12b are parallel to one another, it again being noted that initially thepallet 10 is cantilevered from the main track rails 11a, 111) asindicated in FIGS. 4 and 7, and it is desired to shift the cantileversupport from the main track to the side track, the shiftable bar 24 ismoved from left to right-as viewed in FIG. 4. Such movement of the bar24 will bring the various operating parts into the position shown inFIG. 5. Movement of the bar 24 may be accomplished by any conventionalmeans such as an air operated plunger generally indicated at 29 in FIG.4. Movement of the bar 24 from the left-hand position shown in FIG. 4 tothe right-hand position shown in FIG. 5 results in the roller 27 movingaway from the depending cam surface 22 of the back cam plate 21 fixed tothe arm 19a while the cam roller 28 will move into contact with the camsurface 23, also a part of the cam plate 21, whereby to rock the plate21 and arm 19a in a counterclock-wise direction along with the rod 20.This movement of the arm 19a, and also of the similar arm 19b which isfixed on the rod 20 as earlier described, brings the clamping rollers 17out of contact with the upper main track rail 11a while simultaneouslybringing the clamping rollers 18 into clamping engagement with the upperside track rail 12a whereby the pallet 10 is cantilevered from the sidetrack 12a, 1212 by virtue of the rollers 14 and 16 in cooperation withthe clamping rollers 18. As noted earlier, this shift of the pallet 10from its cantilevered support from the main track 11a, 11b to itssimilar cantilevered support from the side track 12a, 12b occurs whenportions of the main track and side track are parallel to one another.Continued movement of the pallet 10 in a manner to be described shortlyresults in the pallet moving along the side track 12a, 12b into positionbefore an appropriate work station. This is generally indicated in FIG.6 and is shown in somewhat greater detail in FIG. 3.

The pallet 10 is driven by means of one or more downwardly extendingarms generally indicated at 30 in FIGS. 1 and 2; these arms arepreferably spring loaded as shown in these Figures. Fastened to thelower ends of these arms is a plate 31 having some sort of frictionmaterial on the underside thereof. This spring loaded friction plate 31frictionally engages the top of a flat segmented (crescent) chain, whichis well known in the art, and which is disposed beneath the pallet ascantilevered from the main track 11a, 11b. This chain is continuouslydriven at a constant speed by conventional means, not shown, duringoperation of the palletconveyor mechanism. The spring loaded arms 30 andfriction plate 31 cooperate with the roller 13, 15 and 17 to support thepallet 10; the arms 30 and plate 31 aid in stabilizing such pallet as itis moved along the tracks provided for it. The chain itself is generallyindicated at 32 in FIGS. 1 and 3.

Turning now to FIG. 3, a series of work stations is illustrated ascomprised of the mechanisms generally indicated at 33a, 33b and 33c.These work stations are only diagrammatically illustrated in that theymay take any ofa great variety of forms. An object of the invention isto divert the pallet 10 from the main track 11a, 11b to these workstations successively by reason of the side tracks 12a, 12b and theconstructions heretofore detailed. As illustrated in connection with thework station 33a, there is a side track 12a, 12b which brings the pallet10 into proper position with respect to this station. A side conveyorchain 34, which is like the segmented chain 32 and which runs at thesame speed, furnishes the motive power from moving the pallet 10 alongthe side track 12a, 12b when it is cantilevered thereto as herein beforedescribed. As mentioned before, and as shown at 12c and 12d, portions ofthe side track 12a, 121) are parallel to portions of the main track 11a,11b. The chain 32 and 34 also parallel one another in these regions.Just as the rail 12a is at the same level as the rail 110, so is thechain 34 at the same level as the chain 32. The plate 31 is of suchwidth that it extends outwardly beyond the chain 32. Thus, when thepallet is moved into the region at which the track portion 12c isparallel to the rail 11a and at which time the chain 34 is parallel to,and adjacent to, the chain 32, such plate 31 will engage the chain 34while it is still engaged with the chain 32. It will be apparent,therefore, that for a relatively brief period not only is the palletsupported from the main track 11a, 11b and side track 12a, 12b (in thevicinity, for example, of the side track portion 120) but also suchpallet 10 is driven by both the chains 32 and 34. It is at this pointthat the bar 24 is actuated so as to move the combined arm 19a and camplate 21 from the position of FIG. 4 to that of FIG. 5 whereby todisengage the pallet 10 from cantilevered support on the main track 11a,11b and to effect a similar cantilevered engagement of the pallet 10 onthe side track 12a, and 12b.

It will be apparent, therefore, that continued movement of the chains 32and 34 will result in the pallet 10 moving along the side track 12a, 12bto the work station, for example, 33a. Appropriate mechanism, not shown,will be employed to stop the pallet in proper position beneath theworking mechanism at the station 33a. Such means are conventional inconveyor systems.

It will be understood that the arrangement just destood that the pins44a, 11, c and d located at different heights, are designed to actuateswitch mechanisms according to the particular work station that thepallet is to be guided next. The pin and its respective mechanism willactuate the air operated plunger 29 previously mentioned whereby to atthat point effect transfer of the pallet 10 from its cantileveredposition on the main track 11a, 11b to similar cantilevered position onthe particular side track l2a,l2b selected as determined by position ofthe involved pin 44. Other conventional mechanism will stop movement ofthe pallet 10 and lock it in place under the particular work station 33selected. The air cylinder 37 and related mechanisms, although shown inFIG. 1 as positioned under the main track chain 32, will normally beassociated with the side track chain 34 so that when the pallet 10 islocked beneath a work station 33, actuation of the air cyclinder 37 willcause the friction plate 31 to be urged against its spring means and outof drag contact with the flat segmented (cresent) chain 34 so as toprevent wear on this plate. When the pallet is unlocked and the plate 31again brought into contact with the chain 34, the pallet will move alongthe side track until it reaches, for example, side track portion 12dwhich is parallel to the main track 11a. Mechanisms similar to thosepreviously described will actuate another air operated plunger 29whereby to actuate the bar 24 and move it work stations 33a, 33b and330, for lifting the friction plate 31 from contact with the sideconveyor 34 when the pallet has been stopped, so as to cut down wear onthe friction material provided for this plate. Such mechanism mayinclude an air cylinder 37, a pair of rods 38 and 39 pivoted toappropriate frame structure as indicated at 40 and a pivoted connectionof the rod 39 to the plate 31 as indicated at 41. The cylinder 37 willalso be pivoted to appropriate frame structure as indicated at 42. Theupper ends of the arms 39 have pins 43 extending therefrom to a positionbeneath the plate 31. When the pallet il0 is stopped in position beneatha work station such as indicated at 33a by conventional means as earlierindicated, the air cylinder 37 will be actuated in a known mannerwhereby to move the arm 39 so as to lift the plate 31 from the chain itheretofore engaged.

The parts conveyor pallet 10 and related mechanism may include otherfeatures or benefit in conveyor systems. When, for example, it isdesired to switch the pallet 10 from the main track to a selected sidetrack, this may be accomplished by providing the pallet with a series ofactuating pins 44a, b, c, and d located at different heights, one foreach work station, which pins will engage appropriate hammer mechanism,at such time as the pallet 10 is riding on both the main track and aside track, whereby the plunger 29 will be actuated to strike the bar 24and shift it, for example, from the position of FIG. 4 to that of FIG. 5whereby to effect transfer to the pallet 10 from cantilevered engagementon the main track to similar cantilevered engagement on the side track.The details of this mechanism are not shown.

Considering the pallet and conveyor mechanism generally, although notshown in detail, it will be underfrom the right-hand position shown inFIG. 5 to the lefthand position shown in FIG. 4 so that the pallet willagain be supported in cantilever fashion from the main track 11a, 11b.The spring loaded friction plate 31 which extends beyond the side trackchain 34 will at this time be in engagement with the main track chain 32whereby the pallet will now continue its movement on the main trackuntil shunted to another side track for performance of another operationby another work station, such further transfer of the pallet from themain track to a side track to be accomplished as described in connectionwith the station 33a.

It will be apparent to those skilled in the art that modifications maybe made in this invention without departing from the scope and spiritthereof. Although the invention has been described in terms ofparticular structures, mechanisms and arrangements, this has been donefor exemplary purposes only and the invention is not to be limited tothese unless they are specifically set forth in the subjoined claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A pallet adapted to be supported in cantilever fashion from a maintrack comprised of a first pair of parallel, vertically alignedelongated members, said pallet comprising a body, a pair of first upperrollers journaled in said body at one side thereof, a pair of firstlower rollers journaled in said body at said one side, and a first pairof clamping rollers mounted'in said body for selective movement towardsand away from said first upper rollers, each of said first clampingrollers being journaled on a separate arm, both said separate arms beingfixed on a common shaft rotatably mounted in said pallet forsimultaneous movement with said shaft when said shaft is rotated, andmeans to rotate said shaft, whereby when said first upper rollers areengaged on one of said elongated members and said first lower rollersare engaged on the other of said elongated members, movement of saidfirst clamping rollers into engagement with said one of said first pairof elongated members will result in said pallet being cantilevered fromsaid main track.

2. The pallet of claim 1 in which there is a pair of second upperrollers journaled in said body at an opposite side thereof, a pair ofsecond lower rollers journaled in said body at said opposite side, and apair of second clamping rollers, said pair of second clamping rollersbeing movable towards and away from said pair of second upper rollers,whereby said pallet may be selectively cantilevered from tracks locatedadjacent said one side and adjacent said opposite side.

3. The pallet of claim 2 in which each of said second clamping rollersis journaled on the respective one of said separate arms, whereby whensaid first pair of clamping rollers moves towards said first pair ofupper rollers said second pair of clamping rollers moves away from saidsecond pair of upper rollers and vice versa.

4. The pallet of claim 3 in which said means to rotate said shaftcomprises a cam plate fixed to one said separate arm, said cam platehaving a cam surface thereon, and a shift bar slidably mounted in saidpallet, said shift bar having contact means to contact said cam surface,whereby when said shift bar is slid in said pallet so that said contactmeans strikes said cam surface, said cam plate, said separate arms andsaid rod are rotated to bring said first clamping rollers intoengagement with said one of said elongated members, and whereby whensaid shift bar is slid in said pallet in an opposite direction, saidfirst pair of clamping rollers is moved out of engagement with said oneof said elongated members and said second pair of clamping rollers ismoved towards said second pair of upper rollers.

5. The pallet of claim 1 in which said means to rotate said shaftcomprises a cam plate fixed to one said separate arm, said cam platehaving a cam surface thereon, and a shift bar slidably mounted in saidpallet, said shift bar having contact means to contact said cam surface.whereby when said shift bar is slid in said pallet so that said contactmeans strikes said cam surface, said cam plate, said separate arms andsaid rod are rotated to bring said first clamping rollers intoengagement with said one of said elongated members.

1. A pallet adapted to be supported in cantilever fashion from a maintrack comprised of a first pair of parallel, vertically alignedelongated members, said pallet comprising a body, a pair of first upperrollers journaled in said body at one side thereof, a pair of firstlower rollers journaled in said body at said one side, and a first pairof clamping rollers mounted in said body for selective movement towardsand away from said first upper rollers, each of said first clampingrollers being journaled on a separate arm, both said separate arms beingfixed on a common shaft rotatably mounted in said pallet forsimultaneous movement with said shaft when said shaft is rotated, andmeans to rotate said shaft, whereby when said first upper rollers areengaged on one of said elongated members and said first lower rollersare engaged on the other of said elongated members, movement of saidfirst clamping rollers into engagement with said one of said first pairof elongated members will result in said pallet being cantilevered fromsaid main track.
 2. The pallet of claim 1 in which there is a pair ofsecond upper rollers journaled in said body at an opposite side thereof,a pair of second lower rollers journaled in said body at said oppositeside, and a pair of second clamping rollers, said pair of secondclamping rollers being movable towards and away from said pair of secondupper rollers, whereby said pallet may be selectively cantilevered fromtracks located adjacent said one side and adjacent said opposite side.3. The pallet of claim 2 in which each of said second clamping rollersis journaled on the respective one of said separate arms, whereby whensaid first pair of clamping rollers moves towards said first pair ofupper rollers said second pair of clamping rollers moves away from saidsecond pair of upper rollers and vice versa.
 4. The pallet of claim 3 inwhich said means to rotate said shaft comprises a cam plate fixed to onesaid separate arm, said cam plate having a cam surface thereon, and ashift bar slidably mounted in said pallet, said shift bar having contactmeans to contact said cam surface, whereby when said shift bar is slidin said pallet so that said contact means strikes said cam surface, saidcam plate, said separate arms and said rod are rotated to bring saidfirst clamping rollers into engagement with said one of said elongatedmembers, and whereby when said shift bar is slid in said pallet in anopposite direction, said first pair of clamping rollers is moved out ofengagement with said one of said elongated members and said second pairof clamping rollers is moved towards said second pair of upper rollers.5. The pallet of claim 1 in which said means to rotate said shaftcomprises a cam plate fixed to one said separate arm, said cam platehaving a cam surface thereon, and a shift bar slidably mounted in saidpallet, said shift bar having contact means to contact said cam surface,whereby when said shift bar is slid in said pallet so that said contactmeans strikes said cam surface, said cam plate, said separate arms andsaid rod are rotated to bring said first clamping rollers intoengagement with said one of said elongated members.